The invention relates to improvements in apparatus for transverse cutting of webs or strips of paper, plastic sheet stock, metallic foils, or the like. In particular, the invention relates to a means for operating a cutting knife at high speeds. The invention is applicable to the transverse cutting of webs of a variety of materials and in a variety of settings.
Web production methods are used for producing items in which the raw materials are supplied as webs—long continuous strips of thin material. Various processes may be performed on the web of material to produce a product. The web may move continuously through a process or the web may be advanced to a process and then stopped while the process is performed. At some point, the web is cut apart to release the individual product from the web. If multiple products are produced across the width of the web, they may be separated by slitting knives that cut the web along the direction of travel, typically as a continuous operation as the web advances through the slitting process. The products that are produced sequentially along the length of the web may be separated by a transverse cutting operation, which is typically the last step of web production. The transverse cutting may cut a single web or a number of webs produced by slitting in an earlier process. The transverse cutting speed may be a limiting factor in the overall rate of production that can be achieved by a web production method.
A pouch making machine as disclosed in U.S. Pat. No. 5,800,325 is an example of a web production method that employs a transverse web cutter. FIG. 1 is a schematic side view of an exemplary pouch making machine. The pouches fabricated by the machine of FIG. 1 start out as two webs of pouch material 11 and 12. These two webs are joined by being seamed together to form a single web 110. The seaming iron 18 used to create the perimeter seams on the pouches may simultaneously form the seams for a number of pouches along the length of the web 110. The seaming iron may be any number of pouches wide, as is economical under the circumstances. The two webs of sheet stock 11 and 12 are fed into the pouch making machine from two rolls 13 and 14. The webs 11 and 12 are drawn into the machine by rollers 15/16. One or both of these rollers are driven by a motor 17. The motion is intermittent in that the webs are drawn rapidly into the machine for a period of time, and then the motion stops for some other period of time to allow the perimeter seams of the pouches to be made by the hot seaming iron 18 being pressed against a platen 19. The seaming iron 18 is pressed against the platen 19 by one or more hydraulic or pneumatic actuators 22 under the control of a first control system 21. A sensor 20 may provide a signal to the first control system 21 to indicate the position or speed of the web. A typical duration for the seaming process and subsequent cooling is about two seconds.
As the rollers 15/16 are drawing the webs 11 and 12 under the seaming iron, the web section on which pouch seams have previously been formed is passed into an accumulator portion of the machine. The accumulator is the portion of the machine between rollers 15/16 and roller 23. As the web 110 is fed into the accumulator, gravity causes a dancer roller 24 to move downward and accommodate the web being fed in. A high limit sensor, such as a photo-detector 32 and light source 34, detects a shortage of web material in the accumulator section. The signal from the high limit sensor may be sent to a controller for one of the adjacent processes to increase the amount of web material in the accumulator section. For example, the second controller 29 may respond to the high limit sensor 32, 34 by slowing a transverse web cutter 10 to increase the amount of web material in the accumulator section. Similarly, a low limit sensor, such as a photo-detector 33 and light source 35, detects an excess of web material in the accumulator section. The signal from the low limit sensor may be sent to a controller for one of the adjacent processes to reduce the amount of web material in the accumulator section. For example, the second controller 29 may respond to the low limit photo-sensor 33, 35 by speeding up the transverse web cutter 10 to reduce the amount of web material in the accumulator section.
While the web is being fed into the accumulator by rollers 15/16, rollers 25/26 withdraw material from the accumulator and feed it to a transverse cutting knife 27, where the individual pouches are cut off the web. Rollers 25/26 are intermittently driven by a motor 28 under the control of a second control system 29, advancing the web one pouch at a time to the cutting knife, and stopping to permit the knife to sever the pouch. A sensor 31 may provide a signal to the second control system 29 to indicate the position or speed of the web. A drive system 30 operates the cutting knife 27 to oscillate the cutting knife from a resting position to an active position and back to the resting position. It is desirable that the cutter be operable over a range of speeds up to a speed that allows pouches to be cut from the web at the same rate as they are produced by the seaming operation.
Generally, it is desirable to operate a cutter at high speeds. However, a higher speed cutter is more expensive to produce. It would be desirable to produce less expensive cutters that operate at higher speeds.